To be honest, creating a fictional tree can be pretty time-consuming but definitely worth it. What you can do is:
Select the founder of the family tree (in your case, Harry) and under Click to add your relatives on the left-hand side of the screen, select the Add partner/ex button
Select the founder's partner and under Click to add your relatives, select the Add parents button
From here on, you can continue expanding on the relatives (as long as they have some sort of connection to a name on the tree)
In response to your edit, unfortunately, Family Echo won't show the entire tree in the way that you want because it'd be too confusing (as you'll know based on their FAQ page), but you can view each person's branch up to 15 generations (which can be selected through Show options) by opening more tabs of the same family tree. Just remember to save your tree with every edit!